Glued ledger head

ABSTRACT

A modular scaffold component of different material components advantageously uses the durability and reliability of conventional type steel ledger heads adhesively secured to by an aluminum or aluminum alloy structural member. In a preferred embodiment the structural member is an extruded elongate tube and in a further preferred structure the elongate tube is of a non circular cross section having thickened top and bottom portions preferably interior to a circular outer surface. These thickened portions provide additional strength and structural characteristics such that the component can be freely substituted for the equivalent steel component. In this way the component may be added to existing systems to take advantage of the reduced weight thereof without requiring a dedicated system or rendering an existing system obsolete.

FIELD OF THE INVENTION

The present invention relates to components for modular scaffoldingsystems and in particular relates to components made of two differentmaterials.

BACKGROUND OF THE INVENTION

Modular scaffolding systems are extensively used in the building andrepair industries and provide safe and efficient access to elevatedareas. Modular scaffolding systems have advantages over the conventionaltube and clamp systems in that the components connect to one another atpredetermined positions and the systems are more cost effective to erectand tear down.

Typically modular scaffolding systems are made of galvanized steelcomponents. There are a number of well known proprietary arrangementsthat allow the components to be securely fixed to each other. In mostcases the systems are not cross compatible.

Galvanized steel is the material of choice as it is robust and able towithstand shock impacts and provide good structural strength required tosupport the loads that are applied to the scaffolding from wind,materials and personnel.

In some industries there is an increasing tendency to favour the use oflighter weight scaffolding systems in general and in particular to usealuminum scaffold products. For example, aerospace applications andcomputer/IT applications often use aluminum scaffolding products as suchcomponents are lighter in weight and if accidentally dropped are lesslikely to cause extensive damage to the surroundings compared to theheavier galvanized steel product.

All aluminum modular scaffolds have not been considered acceptable forindustrial applications (such as refineries) as the end connections(ledger heads etc.) of these components are prone to damage or need tobe of a significantly larger size to resist abuse and shock loads thatare common in the work place. In Canada the use of aluminum scaffoldproducts in the industrial market has generally been restricted toaluminum tube and clamp systems that use aluminum tube and steel tubecouplers.

Although aluminum scaffolding systems have not been generally accepted,such systems are considered desirable due to the lighter weight of thecomponents. Workers who are erecting the system or tearing it downcertainly prefer the lighter weight of the components. Therefore ingeneral the assemblers would prefer to use lighter weight components forease of assembly however the actual labour component for erectingaluminum tube and clamp systems is much higher.

A hybrid system that proposed using steel connecting heads mechanicallypinned or fastened to aluminum tubes was not successful or accepted asthe softer aluminum tube deforms at the pin or fastening pointcompromising the mechanical connection and rendering the system prone todamage.

The present invention seeks to overcome a number of deficiencies withrespect to the prior art and advantageously use a combination of steelelements secured to aluminum tubes to provide a system which is botheffective and convenient to install due to the reduce weight thereof.

SUMMARY OF THE INVENTION

A modular scaffold component according to the present inventioncomprises first and second steel ledger heads with each ledger headincluding a fastening element to mechanically connect the ledger head tospaced scaffold support members. An elongate tube extrusion of analuminum or aluminum alloy is adhesively secured to each ledger head andforms a structural element therebetween. The elongate tube extrusion ineach ledger head has an overlapping sleeve type relationship withopposed overlapping surfaces secured by an adhesive structurallyconnecting the ledger heads and providing a secure mechanical connectionof each ledger head to the tube extrusion for use in a scaffold system.

According to an aspect of the invention the modular scaffold componentincludes a steel tube connecting stub sized for receipt in the elongatetube extrusion with the adhesive securement therebetween.

According to a further aspect of the invention the steel tube connectingstub overlaps with the elongate tube extrusion over at least one and ahalf inches in the length of the elongate tube extrusion.

In a further aspect of the invention the steel tube connecting stub iswelded to a rear surface of the ledger head.

In a modular scaffold component according to the present invention thecomponent includes at least a ledger head and a connected elongate tube.The improvement comprises an adhesive securement of the ledger head tothe elongate tube and each ledger head includes a connecting portionhaving an overlapping sleeve type relationship with an end of theelongate tube. Preferably an adhesive component is provided within a gapof the overlapping sleeve type relationship and forms a distributedmechanical connection of the elongate tube to the at least one ledgerhead. The elongate tube is of an aluminum or an aluminum alloy materialand the ledger head is of a steel material.

In a preferred aspect of the modular scaffold component the adhesive isa two part adhesive forming a permanent rigid connection of the ledgerhead to the elongate tube.

With the present invention it is preferable that the elongate tubeincludes interior reinforcing at the top and bottom thereof to improvethe characteristics of the elongate tube with respect to bending.Reinforcing on the interior is preferred as the outer diameter of thealuminum tube can be the same as an equivalent steel component. Thisallows the composite modular component to be used throughout the systemand in particular allows clamping arrangements used with most modularsystems to also engage the aluminum tube component.

Preferably the reinforcing on the interior of the aluminum tube is alsodesigned to allow a particular registration with the ledger head. Theledger head preferably includes a portion that is inserted into theelongate tube and cooperates therewith to provide a predeterminedregistration. In this way the orientation of the ledger head withrespect to the elongate tube is simplified and the manufacture of thecomponent is also simplified.

Reinforcing of the elongate tube also has the desirable characteristicthat the strength of the component will be the same or approximately thesame as the corresponding steel component. The composite component islighter weight and easier to use, however there is no requirement toretrain the labour or to have a composite component which is of reducedstrength relative to a steel one. Providing a lighter component that isa replacement for the heavier steel component while still providing thesame functionality is a highly desirable feature of the presentinvention.

Adhesive securement of the ledger heads to the elongate tube or otherstructural connecting component of a reduced weight is the preferredarrangement. It is possible to use other arrangements including themechanical securement of these components while providing the particularadvantages. If an alternate arrangement is to be considered a fillertype material is preferable between the connecting portion of the ledgerhead and the tube to avoid play or movement between these components.For example a bonded type filler arrangement can reduce play and canrely on mechanical securement of a pin type connection or dimple typeconnections to maintain the rigidity of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawings,wherein:

FIG. 1 is a schematic view of a ledger as used in scaffolding systems;

FIG. 2 is a partial sectional view of a scaffold ledger showing theconnection of a ledger head to an aluminum tube;

FIG. 3 is a front view of a guard rail component made of generallyaluminum tubes with steel ledger heads for releasable connection to thescaffolding structure;

FIG. 4 is a further view of a scaffold component made of generallyaluminum tubes and having steel ledger head connectors;

FIG. 5 is a side view showing an aluminum tube connected to a ledgerhead having a downwardly extending drop pin;

FIG. 6 is a side view of a scaffold component having an aluminum tubeand an inner steel tube for connection to a scaffold connecting member;

FIG. 7 is a partial perspective view showing the connection of a ledgerhead to an aluminum tube;

FIG. 8 is a perspective view similar to FIG. 7 without a mechanical pinconnection between the ledger head and the aluminum tube;

FIG. 9 is a partial perspective view of an alternate arrangement wherethe aluminum tube includes thickened top and bottom sections and theledger head includes an extending spigot designed to have a particularregistration with the aluminum tube;

FIG. 10 is a view similar to FIG. 9 without a connecting pin;

FIG. 11 is a perspective view of a 5×5 foot scaffold tower with raisedwork platform; and

FIGS. 12 a and 12 b are perspective views of a preferred cast ledgerhead alone in FIG. 12 a and as a cutaway of a completed connection inFIG. 12 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 generally illustrates a ledger 2 that is a modular component thatis commonly used in scaffolding systems and is sometimes used as a bracemember in shoring systems. There are a number of scaffolding systemscommonly used and typically these proprietary systems use their ownarrangement for connecting of a modular bracing component to a scaffoldleg or to a scaffold frame. One common connecting system as shown inFIG. 3 uses a circular connecting rosette 104 that is welded to theuprights 103 of a scaffolding frame 102 at predetermined points. Theserosettes 104 allow convenient connection with a ledger head 4 or 4 a asgenerally shown in FIGS. 2 and 3. A drop wedge 5 passes through theledger head and through the rosette and positively secures the ledgerhead 4 a to the upright 103 of the scaffold frame 102. Typically thedrop wedge 5 is captured or retained in the ledger head. These rosettescan also be used on the uprights of scaffold frame members to simplifyconnection. Other common connection arrangements include a cup and prongtype arrangement where the prong is inserted into an upwardly extendingcup and a top member moves downwardly to retain the prong in the cup. Ascan be appreciated, the present invention as subsequently described canbe used with different scaffolding connecting arrangements and is notlimited to the particular ledger head design shown in the drawings.

Ledgers of the general structure as shown in FIG. 1 are commonly used inmodular scaffolding systems. One of the desirable features of a modularscaffolding system is the convenience and labour saving in erecting thesystem. Modular systems are based on fixed positions of variouscomponents that interconnect in a simplified manner. In contrast, tubeand clamp scaffolding arrangements are custom designed and require moreskilled labour. In modular scaffolding systems it is cost effective touse relatively large spacing between the upright components. Manysystems use a 5 foot, 7 foot or 10 foot bay spacing between frames.Conventional ledgers made of steel tube with a cast or formed steelledger head either end thereof can easily be carried by a labourer andsteel frames can be carried by two labourers.

FIG. 11 is an example of a 5 foot×5 foot tower 200 commonly used in oilrefinery maintenance applications. The tower includes a raised workplatform 202 having guard rails 204 thereabout. The tower includeselongate legs or uprights 206 connected via rosettes to the guard rails204, the ledgers 208 and the diagonal braces 210. The ledgers 208preferably use the higher load carrying capability of the tubes shown inFIGS. 9 and 10. With this arrangement it is not necessary to distinguishbetween steel and steel/aluminum components as the load carryingcapacities are designed to be similar to allow free substitution. In thecase of a 7 foot load carrying ledger a double tube aluminum ledger willbe used. These components all use the steel ledger heads or connectorsin combination with adhesively secured aluminum or aluminum alloy tubes.

In essentially all applications, the workmen used to erect these systemsprefer a small bay spacing as the components are lighter and thereforeeasier to carry and assemble. In applications or industries where thelabour component has a significant influence in determining anacceptable system, the smaller separation distances such as 7 foot bayseparation is often used where it would be more cost effective to usethe larger 10 foot bay spacing. For higher load applications a 5 footbay spacing is used.

In order to overcome this bias while still being able to achieve thedesired labour savings in erecting of a modular scaffolding system, thepresent invention uses aluminum tubes that have a specific connectionwith a steel ledger head or similar steel connecting component.

The ledger head 4 shown in FIG. 2 is of a steel material and can beformed from plate or may be a cast component. The steel of the ledgerhead is desirable due to its high strength and also its tolerance withrespect to potential damage on the work site. These steel ledger headsare very durable and are not prone to damage.

The ledger head 4 as shown in FIG. 2 includes a system connecting end 6which will have the particular shape for engaging the intended modularscaffolding system. In this case there is a central slot 7 whichreceives part of the flange of a connecting rosette 104. A wedge memberwill pass through the center passage 9 to effectively lock the ledgerhead to a scaffold component as shown in FIG. 3.

Directly opposite the system connecting end 6 is the tube connecting end8. This end of the ledger head 4 is designed to cooperate and engage thealuminum tube 14. The aluminum tube 14 replaces the conventional steeltube that would be used for such a ledger. In the structure shown inFIG. 2, the tube connecting end 8 includes an inner stub collar 20 whichis received interior to the steel tube connecting stub 10. The length ofthe steel tube connecting stub 10 is relatively short and is typicallyin the range of 2 to 6 inches. The length of this steel tube connectingstub provides a large adhesive securement area with the aluminum tube14. A suitable adhesive 22 is shown that connects the steel tubeconnecting stub 10 to the end of the aluminum tube 14. The adhesive 22is preferably a two part epoxy type adhesive.

The steel tube connecting stub 10 in this case is shown secured to theledger head 4 by a weld 12. It can also be seen that the inner stubcollar 20 projects into the steel tube connecting stub 10 a sufficientdistance to overlap with the end of the aluminum tube 14. The inner stubcollar 20 provides support for both the connecting stub 10 and the endof the aluminum tube 14. This overlap arrangement provides an effectivecooperation between the elements and opposes shear. The adhesive 22 isselected to provide strong securement of the aluminum tube 14 to theconnecting stub 10. The adhesive is also preferably selected toelectrically isolate the steel tube connecting stub 10 from the aluminumor aluminum alloy tube 14. This reduces the possibility of corrosion dueto the dissimilar metal materials.

It has been found that the adhesive 22 can provide a durable fixedsecurement of the aluminum tube to the ledger head that is not prone todamage. The length of the steel tube connecting stub 10 in a preferredembodiment is of a length of about 2 to 3 inches and provides sufficientarea for adhesive securement of the aluminum tube to the ledger head.This adhesive securement provides effective connection for the designloads for ledgers and other scaffold connecting components. The adhesiveis selected to comply with the appropriate temperature ranges. Forexample, scaffolding systems used in large refineries in northern Canadacan encounter winter conditions of −45° F. whereas scaffolding systemsin the southern United States encounter summer temperatures in excess of100° F. The adhesive is selected to be effective for the temperatureranges and satisfy typical loads caused by dropping or otherwise onsitejob conditions that the components experience at all temperatures withinthe predetermined ranges.

As can be appreciated from a review of FIG. 2, the steel tube connectingstub 10 provides an effective arrangement for distributing forcesexerted on the ledger head to the aluminum tube without damage thereof.

It has been found desirable to increase the wall thickness of thealuminum tube that would otherwise replace the commonly used steel tube.For example, it is common to use a steel tube with a 3.2 mm thicknessand to provide additional strength the aluminum tube has a thickness ofapproximately 3.7 mm. As can be appreciated there will be more aluminummaterial however the overall weight of the ledger will be significantlyreduced. This lighter system component (i.e. the conventional type steelmaterial for the ledger head in combination with an aluminum tube typemember connected thereto) acts as a equivalent component with thedesirable reduced weight. This has significant advantages to theworkforce responsible for erecting and dismantling of such modularsystems. Typically ledgers are divided into load bearing ledgers and nonload bearing ledgers. A 10 foot ledger is non load bearing and thethicker aluminum type is satisfactory for this application. For loadbearing applications common in 5 foot ledgers a different structure ofthe aluminum tube and ledger is used.

From the above, it might be considered that an all aluminum system wouldbe preferable. Unfortunately an all aluminum system with aluminum ledgerheads is prone to damage or the ledger heads must be greatly oversizedto provide the required durability. This results in a component that isless desirable and/or more expensive to make. The steel/aluminum hybridsystem as described herein having steel ledger heads in combination withan elongate aluminum tube extrusion is both cost effective tomanufacture and light weight.

FIGS. 3, 4, 5, 6, 7 and 9 show a ledger connected to a ledger head thatalso includes securing ports for a pin connector to provide additionalmechanical securement of the ledger head to the tube. This pin typeconnection is normally not necessary as the adhesive securement of thecomponents is sufficient, however it does provide a further wellrecognized connection. There may be some reluctance to initially acceptthe high structural integrity of the adhesive securement and therefore amechanical pin connection is also provided. Furthermore the adhesive andmechanical connections complement one another particular duringassembly. For example, the pin connection maintains the position of thecomponents as the adhesive cures or otherwise sets. With the pinconnection the core after initial gluing is reduced. FIGS. 8 and 10 showa ledger head and aluminum tube connection that relies solely on theadhesive securement of the component.

The ledger head as shown in FIG. 2 has been described with respect to aseparate steel tube connecting stub 10. This arrangement is desirablefor existing ledger head designs that can be used directly or requireonly a small modification to receive the steel tube connecting stub. Asthe system becomes more widely accepted it is anticipated that theledger head and the connecting stub 10 will be an integral component ofthe ledger head. In this case the ledger head would not include the stubcollar 20 as basically the stub collar 20 and the steel tube connectingstub 10 are an integral component of the ledger head 4.

The particular connection of the ledger head 4 to the aluminum tube 14can also be used for connecting of other modular dual materialscaffolding components. FIG. 3 shows a guard rail frame 30 connectedbetween two uprights 100 and 102 shown with rosette connections 104.This is one particular type of scaffolding connection system however itcan be appreciated that other arrangements are also possible. In thiscase the upper rail of the guardrail frame 30 includes steel ledgerheads 4 a including drop wedges 5. The steel connectors 4 b associatedwith the lower rail of the guard rail frame 30 are drop pin connectorshaving a fixed extending pin 9 which is received in a slot of therosette 104. The upper rail 32, the lower rail 34 and the connectingtubes 36, 37 and 38 are of an aluminum tube construction. The connectionbetween the upper rail 32 and its connecting components are similar tothe structure as described in FIG. 2. This is also true for the lowerrail 34 and the connectors 4 b.

As can be appreciated from a review of FIG. 3, the ends of the guardrail frame 30 (i.e. the connecting components 4 a and 4 b) are of aconventional steel configuration and are typically of galvanized steel.These connections provide a robust structure that is not prone todamage. The intermediate components connecting these connectors to theuprights 100 and 102 are of a lighter weight aluminum tubing and as suchthe guard rail frame 30 will be of significantly reduced weight relativeto a similar guard rail frame that uses steel tubing.

FIG. 5 shows further details of the connector 4 b shown in FIG. 3. Thisconnector includes an inner steel tube connecting stub 10, an outeraluminum tube 14 and a suitable adhesive provided between these twocomponents. A connecting pin 15 has been shown.

An aluminum frame 40 is shown in FIG. 4 attached to steel verticalmembers of a scaffold frame 100 and 102. The tubular members of theframe 40 as well as the center connecting member are of an aluminummaterial and thus provide a significant weight advantage. The downwardlyangled diagonal tubes 42 and 44 are also of aluminum and connected tothe short aluminum tube 46 and 48 associated with the steel leg engagingmembers 47 and 49. This aluminum frame provides the weight advantageswhile still providing good load bearing capabilities. Designing thecombination steel/aluminum components to have equivalent strength as theexisting steel components allows mixing of components without regard totype.

The connector 110 shown in FIG. 6 includes the outer aluminum tube 14 incombination with the inner steel tube connecting stub 10. Thesecomponents are secured by an adhesive. The end 112 of the steel tubeconnecting stub 10 has been adapted for welded securement to a similarsteel tube. As can be appreciated the steel tube connecting stub 10 cantake different configurations appropriate for connection to a steelcomponent.

Additional details of the hybrid system can be appreciated from a reviewof FIGS. 7, 8, 9 and 10. FIG. 7 shows the described connectionarrangement with two ports for receiving a connecting pin that is usedin addition to the adhesive securement. FIG. 8 is a prospective viewessentially the same as FIG. 7 but without a connecting pin securement.Adhesive securement can be supplemented with a mechanical securement tomeet any design or safety requirements. As a steel stud or tube isstronger than an equivalent sized aluminum tube, it is generallypreferred to have the aluminum tube sleeve the steel connecting stud ortube. This relationship can be reversed as the more important issue isthe adhesive securement therebetween.

The structures of FIGS. 9 and 10 are similar to FIGS. 7 and 8 howeverthe cross section of the aluminum tube has been modified. FIG. 9 againincludes ports for a connecting pin whereas FIG. 10 relies solely on theadhesive securement. Other securing arrangements can be used incombination with the adhesive if desired, however the adhesive on itscan provide the required strength as the adhesive securement area can beincreased when necessary.

In FIGS. 9 and 10 both the steel tube connecting stub 10 a and thealuminum tube 14 a have been modified to provide several advantages.Basically the ledger head with the steel tube connecting stub securedthereto can only be received in the modified aluminum tube 14 a in oneof two orientations. With this arrangement it is easy to assemble theledger heads to the aluminum tube and provide accurate alignment of thetwo ledger heads.

The modified cross section of the aluminum tube 14 a provides additionalstrength with respect to bending. A thickened portion is provided at thetop surface of the modified aluminum tube 14 a and the bottom surface ofthe tube has also been increased. This structure provides a reinforcedor higher strength top and bottom flange joined by the side members.Similarly the connection to the ledger head is also improved. Thismodified tube also cooperates with the ledger head to provideregistration and thus simplifies assembly of the components. The steeltube connecting stub 10 a includes a top and bottom surface that closelycorresponds to the modified tube 14 a to provide the registrationfunction.

A modified ledger head 304 is shown in FIGS. 12 a and 12 b and is a onepiece cast steel material with the connecting stub 310 including aflattened top surface 330 and a corresponding flattened bottom surface332.

The sides 340 and 342 of the connecting stub 310 each include a pair ofshallow grooves 336 and 338 that preferably have a depth ofapproximately 2 mm. The grooves 336 and 338 are positioned either sideof the connecting port 350. Each of the sides 340 and 342 include acenter flattened portion 354.

The purpose of the flattened portions 354 and the shallow grooves 336and 338 are to assist in the distribution of the adhesive (preferably anepoxy adhesive and most preferably an acrylic epoxy adhesive). Theseflattened portions 354 and the grooves 336 and 338 provide channels thatallow the epoxy to flow and provide a large adhesive securing surfaceabout the connecting stub 310. As can be appreciated from a review ofFIG. 9, the modified aluminum tube extrusion 14 a includes a flattenedtop surface 360 and bottom surface 362 interior to the pipe for closelyengaging surfaces 330 and 332 of the cast ledger head. These grooves andflattened area provide additional space to receive excess epoxy whilestill providing efficient coating about the connecting stub. In additionthese grooves will act to further improve the attachment of the tube tothe ledger head. As can be appreciated, the ledger head of FIGS. 9, 10,12 a and 12 b with the modified aluminum pipe extrusion as shown inFIGS. 9 and 10 provide a simple arrangement where the ledger heads areregistered with the tube and thus improve the assembly of thecomponents. The grooves 336 and 338 provided either side of theconnecting stub in combination with the flattened portions 354 alsosimplify securement of the ledger head to the tube and also assist inproviding excellent locking of the ledger head to the tube extrusion.FIG. 12 b shows a completed connection.

The modified tube extrusion as shown in FIGS. 9 and 10 include thethickened top area 380 and the thickened bottom area 382 that providesadditional strength for the tube extrusion to oppose bending of the tubein the vertical plane assuming the tube was horizontal. These act in away similar to the top and bottom flanges of an I-beam type shape. Thesize of the areas 380 and 382 can be adjusted to provide the desiredstructural characteristics of the tube while also simplifying theregistration of the ledger head with the tube. The opposed curved sidewalls 384 and 386 of the tube 14 a closely correspond to the side walls340 and 342 of the ledger head. These sidewalls are somewhat thinner,preferably about 3.20 mm with an outside tube diameter of 48.30 mm.

It is highly desirable to maintain the common outside steel tubediameter of 48.30 mm to allow compatibility with a host of existingclamps and other components designed for this tube diameter.

The following is a comparison of a ten foot aluminum ledger with themodified tube extrusion shown in FIGS. 9 and 10 to an all steel ten footledger:

Aluminum Bearer Regular w/Glued Steel Ledger Limiting Attribute LedgerHeads Factor Weight of Aluminum 10 ft 11.1 5.98 — Ledger c/w ledgerheads and wedges (kg) Calculated Safe Bending 0.50 0.52 Allowable Moment(kN · m) Bending Stress in Tube End Vertical Load 8.9 8.9 RosetteCapacity (kN) Capacity Safe tensile strength 14.19 14.19 Rosette/Wedgeof ledger head to Capacity rosette connection (kN)

Ten and seven foot ledgers are not designed for substantial loadcarrying capability. In contrast a five foot steel ledger is oftenreferred to as a bearer for significant load carrying capacity. Themodified aluminum tube ledger is designed to have properties generallythe same as the conventional steel tube and significantly stronger thanconventional or regular aluminum scaffold tube.

The following tables provide a comparison of the modified aluminum tubeto a regular aluminum tube, an equivalent high strength aluminum tubehaving a thickened wall to provide properties similar to a conventionalsteel tube and the conventional steel tube section.

REGULAR ALUMINUM SCAFFOLD TUBE

SECTION PROPERTIES SECTION MODULUS: 5330 mm{circumflex over ( )}3 MOMENTOF INERTIA: 128730 mm{circumflex over ( )}4 WEIGHT: 1.392 kg/m OPTIMIZEDALUMINUM LEDGER TUBE

COMPARISON TO REGULAR ALUMINUM SECTION PROPERTIES SCAFFOLD TUBE SECTIONMODULUS: 7746 mm{circumflex over ( )}3     45% Stronger MOMENT OFINERTIA: 187085 mm{circumflex over ( )}4     45% Stiffer WEIGHT: 1.872kg/m     34% Heavier

The table above shows the section properties of aluminum scaffold tube,commonly used in Canada, compared to the optimized version referred toin the present patent application. It can be seen that, although theoptimized version is 34% heavier, it is 45% stronger and 45% stiffer.The optimized section is as strong as the regular steel scaffold ledgertubes when subjected to bending stresses.

EQUIVALENT STRENGTH ALUMINUM TUBE

SECTION PROPERTIES SECTION MODULUS: 7746 mm{circumflex over ( )}3 MOMENTOF INERTIA: 187085 mm{circumflex over ( )}4 WEIGHT: 2.249 kg/m OPTIMIZEDALUMINUM LEDGER TUBE

COMPARISON TO REGULAR ALUMINUM SECTION PROPERTIES SCAFFOLD TUBE SECTIONMODULUS: 7746 mm{circumflex over ( )}3 Identical strength MOMENT OFINERTIA: 187085 mm{circumflex over ( )}4 Identical Stiffness WEIGHT:1.872 kg/m 17% lighter

The table above shows the section properties of an aluminum scaffoldtube with a constant wall thickness and with the same strength andstiffness as the optimized aluminum ledger tube. It can be seen that,because the aluminum is not distributed in the most favourable manner,the regular tube is 17% heavier compared to the optimized section.

STEEL SCAFFOLD LEDGER TUBE

SECTION PROPERTIES SECTION MODULUS: 4774 mm{circumflex over ( )}3 MOMENTOF INERTIA: 115292 mm{circumflex over ( )}4 WEIGHT: 3.539 kg/m OPTIMIZEDALUMINUM LEDGER TUBE

COMPARISON TO REGULAR ALUMINUM SECTION PROPERTIES SCAFFOLD TUBE SECTIONMODULUS: 7746 mm{circumflex over ( )}3     62% Higher MOMENT OF INERTIA:187085 mm{circumflex over ( )}4     62% Higher WEIGHT: 1.872 kg/m    47% Light er

The table above shows the section properties of a typical steel scaffoldledger tube with the same bending strength as the optimized aluminumledger tube. It can be seen that the optimized aluminum ledger tube is47% lighter compared to the steel tube.

As can be seen the modified tube is lighter and structurally stronger byproviding more material on the interior of the top and bottom areas ofthe tube (preferably of equal size). The side walls have been slightlyreduced (relative to conventional aluminum tube) to a thickness of 3.20mm.

From the above, it can be seen that the safe load capacities of ledgersis limited by the strength of the rosette connection. This means thatthe performance of the aluminum ledger is equivalent to steel ledgers.The aluminum ledger will deflect more under load, but there is noregulatory limit imposed upon the maximum allowable deflection ofscaffold ledgers. As can be appreciated as the length of the ledgerdecreases the strength will increase as it is preferred to use the sametube extrusion. With this arrangement the aluminum bearer with gluedledger head can be freely used as a replacement for the conventional allsteel bearer.

Two part acrylic adhesives are normally available in different gradeshaving different working times. The adhesive is preferably selected tobe operative once cured in a temperature range from −40° C. to 149° C.Desirably the adhesive resists dilute acids, alkalies, solvents,greases, oils, moisture, salt spray and weathering. Furthermore it ispreferable that the adhesive is nonconductive and provides an electricalinsulating property separating the steel ledger head from the aluminumtube and thus reduces possible galvanic action therebetween.

Due to the scaffold application the adhesive must be tolerant tovibration and a more flexible adhesive is preferred. More brittleadhesives can crack under impact load that can occur by dropping orstriking with a hammer that may occur during connection to a scaffoldleg.

Two suitable adhesives for the glued ledger head and pin structure areas follows:

Adhesive 1: Manufacturer: Extreme Adhesives Inc. Type: Methacrylate2-part Adhesive System Product Name: Extreme 310 Shear strength 3,300psi as rec'd aluminum): Tensile Elongation: 60% Thermal Service −65 F.to +260 F. Range: Mix Ratio: 1:1 Working Time 13 to 17 minutes at 75degrees F.): Colour: Straw or Black Clean-up Solvents: MEK, Acetone

Adhesive 2: Manufacturer: Parsons Adhesives Inc. Type: Methacrylate2-part Adhesive System Product Name: 7120 Shear strength 3,000 to 3,300psi as rec'd aluminum): Tensile Elongation: 45% to 50% Thermal Service−40 F. to +260 F. Range: Mix Ratio: 1:1 Working Time 120 to 130 minutesat 75 degrees F.): Colour: Cream or White Clean-up Solvents: MEK,Acetone

It is believed an appropriate amount of tensile elongation is desired toavoid brittle fracture of the adhesive by vibration or shock load duringuse of the components. A tensile elongation of the adhesive of at leastabout 20% is considered appropriate. The preferred adhesives above havemuch higher elongation and still provide sufficient tensile strength inexcess of 20,000 lbs. The following is an example of the assemblyprocedure:

Surface Preparation:

IMPORTANT: In order to maximize joint strength, preparation of the jointmating surfaces take place preferably not more than two hours beforeassembly or as specified by the manufacture. Preparation of the surfacesand the timing thereof are chosen to achieve effective bonding of thecomponents.

STEP 1: Clean the ends and interior surfaces of the aluminum ledger tubeand the mating surfaces of the ledger head castings with MEK or Acetonefor a length of 2″. Allow to dry.

STEP 2: Abrade the internal mating surfaces of the aluminum bearer witha flapper wheel or by hand sanding using 100 grit abrasive paper.Carefully remove all grit and dust from inside the ledger tube.

STEP 3: Carefully abrade the galvanized mating surfaces of the ledgerhead by hand using 100 grit abrasive paper, taking care not to breakthrough the zinc galvanized coating.

Application of Adhesive:

Note: To be undertaken in a working temperature of 70 degrees F. to 75degrees F.

STEP 4: Mix a sufficient amount of adhesive in accordance with themanufacturer's recommendations.

STEP 5: To achieve an even layer of adhesive, trowel the material ontoboth ledger heads and inside the aluminum extrusion using a 24 tpihacksaw blade, or similar, as the trowel.

STEP 6: Apply adhesive to all mating surfaces inside both ends of thealuminum profile, for a length of at least 2″, making sure that there isa build-up at the curved inside portions on the inside of the aluminumprofile (where there is a wall thickness 3.2 mm). Adhesive must also beapplied to end surfaces of the aluminum profile to provide a sealedjoint against the rear of the ledger head casting.

STEP 7: Apply the adhesive to the mating surfaces of both ledger heads,making sure that all surfaces are covered and that there is a build-upof adhesive on the curved sides of the ledger head mating surfaces.Adhesive must also be applied to the flat mating surface where the endof aluminum ledger tube will butt against the rear of the ledger head.

Assembly of Ledgers:

Note: Assembly must be carried-out within the working time of theselected adhesive, after mixing and in temperatures that comply with theadhesive manufacturer's recommendations.

STEP 8: Push the ledger head fully into the end of the aluminum ledgertube until it will go no further. Ensure that the end of the aluminumledger tube is fully in contact with the flat surface at the rear of theledger head.

STEP 9: Immediately secure the joint with the specified zinc platedsteel coil pin to hold the ledger head in place while the adhesivecures.

STEP 10: Repeat steps 8 though 10 for the second ledger head.

STEP 11: Clean off any excess adhesive that has been squeezed out theend of the aluminum ledger tube during assembly with acetone or MEK.

STEP 12: Secure Wedges to both ledger heads.

STEP 13: Store the assembled ledger assembly horizontally, in a warmarea, during the curing period.

As can be appreciated, particularly with the designs shown in FIGS. 9,10, 12 a and 12 b, the connecting stubs of the ledger heads may becoated with a mixed two part adhesive and then subsequently inserted inan appropriate length of the aluminum tube. Registration of the ledgerhead with the aluminum tube is achieved due to the particularcooperation therebetween. Once the stub is inserted, a suitable pinconnector can be inserted if the ports are provided or the componentsmay merely be maintained in the assembled orientation until such time asthe adhesive has cured. The connecting stub overlaps with the end of thetube 14 a and includes a large area for adhesive securementtherebetween. Basically this area determines the mechanical strength ofthe connection. Furthermore the required skill to make the connection islow and reliability is high.

In the preferred arrangement the entire surface of the connecting stubis coated with adhesive whereby a strong mechanical connection of thecomponents is achieved. The particular level of this mechanicalconnection is a function of the surface area of the adhesive securementbetween the aluminum tube and the ledger head. A connecting stub ofapproximately one and a half inches in length coated thereabout andcooperating with an appropriate sized aluminum tube will provide amechanical securement having a shear strength of 3000 to 4000 psi. Ascan be appreciated there is some tolerance between the connecting stuband the interior of the aluminum tube which is essentially filled by thetwo part adhesive. The two part adhesive will also assist in theinsertion of the connecting stub into the tube. It is anticipated thatif the epoxy has a working time of about 10 to 20 minutes that the epoxycan be dispensed in an automated manner such that the two parts mix uponapplication to the connecting stub and this will provide more thansufficient time to allow the ledger head to be properly positionedeither end of the tube. Typically the assembled parts will be placed ona rack or other suitable structure to avoid inadvertent forces untilsuch time as the epoxy is cured or partially cured.

It is also possible to use the modified aluminum or aluminum alloy tubesection and the cooperating steel ledger heads in a mechanically securedconfiguration. The close fit of the ledger heads in or about thealuminum tube provides a larger area for distributing loadstherebetween. It is preferable to fill any gap or tolerance between theoverlapping surfaces of the tube and ledger head with a filler materialthat need not provide the adhesive securement earlier specified. A pinor other mechanical securement can be used. With this arrangement aledger or other scaffold component that previously used a steelconnecting arrangement can be modified using the modified tube toprovide weight advantages while be generally equivalent or allowingsubstitution for the conventional heavier steel component.

A vertical pin securement through the thickened portions may bepreferred for both the mechanical and the mechanical adhesivesecurement.

With this arrangement it is desirable to provide a mechanical securementthat distributes the load and avoids high stress areas or a looseconnection. It is also desirable to electrically separate the steelledger from the aluminum tube.

In some all steel scaffold systems, a ledger is fabricated as a singlepiece component with the ledger heads formed by cutting and deformingthe ends of the tube. Basically the ends are slotted and flattened toform ledger heads. For this type of system an aluminum/steel systemwould use short steel tubes with integral ledgers adhesively secured toan aluminum tube. In this way the same type of ledger head connection ismaintained.

The present arrangement allows effective integration of steelscaffolding posts or frames that use conventional mechanical connectionof components with the hybrid dual material scaffold components. Theconnecting components such as guard rails, guard rail frames, ledgermembers, diagonal bracing members, and other components which connect tosuch uprights, advantageously use a steel head or connecting portion toform the mechanical connection. The steel connecting components havebeen modified to include an adhesive securement of an aluminum tube toone side of the component. Thus a significant portion of each of theseconnecting members are made of aluminum or aluminum alloy and are ofreduced weight relative to the same component fabricated using steeltubing. Advantageously the system is lighter weight and as such it ispossible to use greater separation between the upright members (morecost effective) or more favorable conditions for the labour erecting thesystem if they choose to use a smaller separation distance betweenuprights.

In refineries in northern Canada modular scaffolding systems are usedextensively and 10 foot base spacings could be used for manyapplications. However in most cases smaller bay separation is used asthe work force assembling the systems prefers the smaller and lighterweight components. The hybrid system as disclosed herein can be used toallow a larger spacing to be used while also providing a system which islightweight and thus more acceptable to the installing workmen. Themodified system does not need to replace all of the existing steelcomponents as the upright members continue to be of steel and only theconnecting components are replaced or added. Furthermore it can beappreciated that the system is fully compatible with a mixture of steeland aluminum hybrid components particularly the reinforced aluminumtubes that are designed to have the same load carrying capacities as theequivalent all steel component. This allows mixing of the systemcomponents without concern regarding different load ratings. Thisprovides a gradual turnover of the equipment to the new hybrid systemcomponents.

Although various preferred embodiments of the present invention havebeen described herein in detail, it will be appreciated by those skilledin the art, that variations may be made thereto without departing fromthe spirit of the invention or the scope of the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A modular scaffoldcomponent comprising first and second steel ledger heads including afastening element to mechanically connect the ledger head to spacedscaffold support members, an elongate tube extrusion of an aluminum oraluminum alloy material adhesively secured to each ledger head andforming a structural element therebetween, said elongate tube extrusionand each ledger head having an over sleeve type relationship withopposed overlapping surfaces secured by an adhesive structurallyconnecting said ledger heads and providing a secure mechanicalconnection of each ledger head to said tube extrusion for use in ascaffold system.
 2. A modular scaffold component as claimed in claim Iwherein each ledger head includes a steel tube connecting stub sized forreceipt in said elongate tube extrusion with said adhesive securementtherebetween.
 3. T modular scaffold component as claimed in claim 2wherein said steel tube connecting stub overlaps with said elongate tubeextrusion over at least one and a half inches in the length of saidelongate tube extrusion.
 4. A modular scaffold component as claimed inclaim 3 wherein said steel tube connecting stub is welded to a rear faceof said ledger head.
 5. A modular scaffold component as claimed in claim3 wherein said steel tube connecting stub and said ledger head are anintegral casting.
 6. A modular scaffold component as claimed in claim 2wherein said component is a ledger, a diagonal brace, a reinforced loadcarrying member, a frame member or a guard rail.
 7. A modular scaffoldcomponent as claimed in claim 1 wherein each ledger head includes aconnecting part that receives an end of said elongate tube extrusion andforms said overlapping sleeve relationship therewith.
 8. A modularscaffold component as claimed claim 7 wherein said adhesive is a twopart adhesive forming a rigid connection of said ledger head to saidtube extrusion.
 9. A modular scaffold component as claimed in claim 7wherein said overlapping sleeve relationship is of a length of at leastone and a half inches.
 10. in a modular scaffold component having atleast a ledger head and a connected elongate tube, the improvementcomprising an adhesive type securement of the ledger head to saidelongate tube, each ledger head including a connecting portion having anoverlapping sleeve type relationship with an end of said elongate tube,and an adhesive component within a gap of said overlapping sleeve typerelationship forming a distributed mechanical connection of saidelongate tube to said at least one ledger head; said elongate tube beingof an aluminum or aluminum alloy material and said ledger head being ofa steel material.
 11. In a modular scaffold component as claimed inclaim 10 wherein said adhesive is a two part adhesive forming apermanent rigid connection of said ledger head to said elongate tube.12. In a modular scaffold component as claimed in claim 10 wherein saidscaffold component is a ledger, guard rail or reinforced ledger and saidcomponent includes at least two ledger heads at opposite ends of saidelongate tube.
 13. In a modular scaffold component as claimed in claim10 wherein said adhesive is an epoxy adhesive.
 14. In a modular scaffoldcomponent as claimed in claim 10 wherein said adhesive forms anelectrical insulating layer sufficient to avoid a dielectric currentbetween said elongate tube and said at least one ledger head.
 15. In amodular scaffold component as claimed in claim 10 wherein saidconnecting portion is tubular and is received in said elongate tube orsaid elongate tube is received in said connecting portion.
 16. In amodular scaffold component as claimed in claim 15 wherein said adhesivecomponent between said connection portion and said elongate tube is atwo part epoxy adhesive.
 17. In a modular scaffold component as claimedin claim 16 wherein said connection portion and said elongate tube havecooperating non circular cross sections requiring a particularregistration of said connection portion and said elongate tube to formsaid overlapped relationship.
 18. In a modular scaffold component asclaimed in claim 10 wherein each ledger head additional includes a pintype mechanical connection of the ledger head to said elongate tube. 19.In a modular scaffold component as claimed in claim 18 wherein the pinconnection of each ledger head when considered independent of saidadhesive securement is of less strength or durability compared to theadhesive securement of the ledger head to said elongate tube.
 20. In amodular component as claimed in claim 10 wherein said sleeve typerelationship extends at least one and half inches in the length andabout an interior or exterior surface of the end of said elongate tube.